440 PROFESSOR A. SCHUSTER AND MR. W. GANNON ON A 
The mean of the first set of three observations gives ‘0935 for the specific heat of 
copper at 59°, and the mean of the last two :0924 for the specific heat at 32°. The 
average temperature at which our observations were made was 19°, and, assuming 
the specific heat to be a linear function, we may with sufficient accuracy adopt for its 
value -0918. The water-equivalent of the calorimeter, taking account of the small 
quantity of gold on it, is thus found to be 14°71. An error of 1 per cent. in this value 
would change our result by one part in ten thousand, and we may certainly trust the 
assumed specific heat of copper to that degree of accuracy. Our heating coil and 
frame were made of brass, porcelain, glass, platinoid, and shellac. After the conclu- 
sion of our experiments the whole of the heating frame, coil, and stirrer was broken 
up and enclosed in a cage of copper gauze, and its water-equivalent determined, with 
the following result :— 



TasLe VII. 
‘ . Water Mean temperature | 
Experiment. - | 1 
equivalent. of copper. 
| 
| : | 
| 
1 9°62 | 27 
2 9°72 29 
3 9°68 27 
4 9:96 57 
5 9°95 58 
6 9:98 58 



From these figures we calculate the water-equivalent at 19° to be 9°59. 
We had originally intended to calculate the water-equivalent of our frame and coil 
by adding the equivalents of its parts, and we had for this purpose made some 
experiments on the specific heat of porcelain and platinoid. The experiments were not 
quite satisfactory, in the first place, because they related to a temperature higher than 
the one used in our experiments, and secondly because when they were made we had 
not quite realised what serious errors may be introduced, even with the best thermo- 
meters when the temperature during the last period is falling. Our values, for this 
reason, were no doubt too high, Although we trust entirely to the water-equivalent 
9°59, which was directly determined with all precautions, and with a thermometer 
rising during the whole course of the experiments, we nevertheless give as a check 
the equivalents calculated from that of its parts. 
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